Some lawn mowers comprise a front mounted mower deck which is connected to the chassis of the lawn mower by means of support arms. The mower deck is the part of the lawn mower which is provided with one or several cutting knifes. The cutting height, i.e. the distance between the plane in which the cutting knifes are rotatably positioned and the ground often need to be variable. This is accomplished by means of some form of cutting height adjustment device.
Wheels are normally provided in front of the mower deck and sometimes also behind the mower deck. The wheels are intended to be in contact with the ground during mowing and support the mower deck as well as maintain a constant distance between the mower deck, i.e. the plane of the cutting knifes and the ground. A mower deck with no front mounted wheels may encounter problems when reaching an up-hill slope, since the front edge of the mower deck may get stuck in the ground and prevent forward motion of the lawn mower.
Moreover, such a wheel is often pivotal about an axis and the centre of the wheel is eccentrically displaced from the axis, so called pivot wheels. The pivot wheels make it easier for the lawn mower to pass around obstacles such as tufts, cf. the wheels of shopping trolleys.
The cutting height adjustment device needs to be coupled to the mower deck and to the wheels so as to adjust the mutual height relationship between the mower deck, i.e. the plane of the cutting knifes, and the centre of the wheels, i.e. the ground. If pivot wheels are employed, the axes which they can pivot about must be kept perpendicular to the ground at all time during mowing. If not, the pivot wheels would assume a preferred position with respect to their axes and their function would be deteriorated.
Several technical solutions have been focused on this problem of adjusting this mutual height relationship at the same time as the pivot axes of the pivot wheels are kept perpendicular to the ground.